Milk is an important source of dietary calcium. Calcium, the most abundant mineral in body, is a major constituent of bone and teeth. This mineral also plays an important role in several physiological systems. Calcium is important for healthy bone and tooth development in the young and therefore an adequate intake is essential. Calcium status may also be a factor in the development of osteoporosis in elderly people.
Since the body does not produce minerals, it is totally dependent on an external supply of calcium, nutritional or supplementary. The importance of adequate calcium intake is recognized during the whole life of the human being. In 1994, the NIH Consensus Development Panel revised recommended daily allowances for calcium intake for each age group from 800-1200 mg per day to 1500 mg per day.
It has been suggested that calcium in association with caseins may improve absorption in the gastrointestinal tract. Also it has been found that organic acids salts of calcium are more bioavailable in general than the inorganic salts. Calcium citrate has advantages over other calcium salts for use in fortified foods because of high bioavailability. For example, calcium citrate, as opposed to calcium in general, has only a marginal effect of interfering with the absorption of other minerals, especially iron. Also, long-term calcium supplementation with calcium citrate can reduce the risk of formation of kidney and urinary stones since citrate ions are inhibitors for crystallization of stone-forming calcium salts.
Addition of calcium to beverages, especially milk, can be very difficult. If slightly or completely insoluble sources of calcium are used, precipitation of the salts can occur especially if stabilizers are not used. If highly soluble sources of calcium (calcium chloride, etc.) are used, interation between the calcium and calcium sensitive ingredients, such as milk protein, can occur. These interactions can lead to coagulation of the ingredients during temperature treatment even at pasteurization temperature. In addition, the pH of some calcium salt systems may not be compatible with other ingredients or affects the flavor.
U.S. Pat. Nos. 4,701,329 and 4,851,243 disclose the use of tribasic calcium phosphate, carrageenan, and guar in calcium- and phosphorous-enriched milk. In this system,the use of stabilizing gums is necessary to prevent sedimentation of the insoluble calcium salt, which also increases the thickness of the milk.
U.S. Pat. No. 4,840,814 involves a process for preparing calcium enriched milk in which the milk is heat-treated prior to soluble calcium salt addition. This requires additional processing, and could also effect the quality of the milk. In addition, this method is limited to allowing only up to a 30 mg % increase in the calcium.
A series of patents such as U.S. Pat. Nos. 4,722,847, and 4,919,963 (and many subsequent patents), disclose the use of calcium citrate-malate complexes for the fortification of beverages, beverage concentrates, and as supplements. These systems are stable when the pH is kept below pH 5. For a number of beverages this pH would result in acidic flavors and instability of proteins, especially milk proteins. This problem is also encountered in U.S. Pat. Nos. 4,871,554 and 5,500,232.
EP 0709033 discloses preparation of calcium-supplemented milk drinks through the use of minerals extracted from whey. Although this creates products with good flavor and stability the level of supplementation is limited to 40 mg %.